1. Field of the Invention
This invention relates to materials for forming a shaped charge liner. More particularly, a single phase alloy of nickel, tungsten and cobalt provides a liner having improved penetration performance and/or lower cost when compared to conventional materials.
2. Description of the Related Art
Shaped charge warheads are useful against targets having reinforced surfaces, such as rolled homogeneous steel armor and reinforced concrete. These targets include tanks and bunkers. Detonation of the shaped charge warhead forms a small diameter molten metal elongated cylinder referred to as a penetrating jet. This jet travels at a very high speed, typically in excess of 10 kilometers per second. The high velocity of the penetrating jet in combination with the high density of the material forming the jet generates a very high amount of kinetic energy enabling the penetrating jet to pierce the reinforced surface.
Similar to the penetrating jet is an explosively formed penetrator (EFP). An EFP is formed from a shaped charge warhead having a different liner configuration than that used to form a penetrating jet. The EFP has a larger diameter, shorter length and a slower speed than a high velocity penetrating jet.
Suitable materials for shaped charge liners to form EFPs and penetrating jets have low strength, low hardness and high elongation to failure. Wrought liners, formed by casting an ingot which is then reduced to a sheet of a desired thickness by a combination of rolling or swaging and annealing, utilize either expensive starting materials such as tantalum and silver or ductile materials having relatively low densities such iron (density=7.8 g/cm3 and copper (density=8.9 g/cm3). Molybdenum (density=10.2 g/cm3) is typically formed using powder metallurgy and hot forged to near-net shape.
As disclosed in U.S. Pat. No. 6,530,326 to Wendt, Jr. et al., liners are also formed from a mixture of a tungsten powder and a powder with a lower density such as lead, bismuth, zinc, tin, uranium, silver, gold, antimony, cobalt, zinc alloys, tin alloys, nickel, palladium and copper. A polymer is added to the mixture to form a paste that is then injected into a mold of a desired liner shape. The liner is then chemically treated to remove most of the polymer and then heated to remove the remaining polymer and to sinter. U.S. Pat. No. 6,530,326 is incorporated by reference in its entirety herein.
An article entitled “Prospects for the Application of Tungsten as a Shaped Charge Liner Material” by Brown et al. discloses shaped charge liners formed from a mixture of tungsten, nickel and iron powders in the nominal weight amounts of 93% W-7% Ni-3% Fe. The powders are mixed, compacted and liquid phase sintered. It is disclosed that liners jets formed from this material broke up rapidly.
Tungsten base alloys having in excess of 90 weight percent of tungsten are conventionally referred to as tungsten heavy alloys (WHA) and have a density in the range of between 17 g/cm3 and 18.5 g/cm3. A WHA that has been used to produce kinetic energy penetrators, fragmentation warheads, radiation shielding, weighting and numerous other products is a mixture of tungsten, nickel, iron and cobalt. The products are formed by using a process of powder compaction followed by high-temperature liquid-phase sintering. During liquid phase sintering, nickel, cobalt and iron constituents of the compact melt and dissolve a portion of the tungsten. The result is a two-phase composite alloy having pure tungsten regions surrounded by a nickel-iron-cobalt-tungsten matrix alloy. It has been observed that the percentage of dissolved tungsten can be high.
There remains a need for a liner material effective to form shaped charge liners and explosively formed penetrator liners that does not have the disadvantage of poor jet performance of the two phase liners described above and also does not suffer from the high cost or low density problems of the wrought liners described above.